The invention relates to an analog/digital converter device for analog/digital converting of at least one analog low-frequency signal and to a method for analog/digital converting of at least one analog low-frequency signal.
A multimedia computer generally includes a sound card for converting a captured analog speech signal, which is input into the computer by a user via a microphone or a line-in-jack, into a digital signal, which digital signal may further be processed by a processing unit, e.g. a microprocessor. For converting the analog signal into a digital signal, an analog/digital converter in the sound card is provided.
However, many of the available sound cards attenuate substantially or even cut off components of the analog signal before the signal is applied to the analog/digital converter for being digitized. Usually, such a sound card has a predetermined border frequency value. The common sound card thus cannot usually detect and process an analog signal with a frequency below this predetermined border frequency value, e.g. it is not possible to capture and process an analog signal with direct-current (DC) signal components. An example of the border frequency value is a frequency of 20 Hz, i.e. many sound cards cannot capture and process an analog signal in a frequency range between 0 Hz and 20 Hz.
Though an audio analog signal usually has a frequency which is above that border frequency value of e.g. 20 Hz, a problem arises when the sound card is intended to be used as well for measurement of non-audio analog signals, as an analog low-frequency signal having frequency components below the predetermined border frequency value cannot be entirely captured by the sound card, since only an analog high-frequency signal which has frequency components only above the predetermined border frequency value and within the frequency range of the sound card can entirely be captured.
An xe2x80x9canalog low-frequency signalxe2x80x9d in this description means a signal with at least one important frequency component below the predetermined border frequency value of the sound card. xe2x80x9cImportant frequency componentxe2x80x9d in this context means that the capturing and processing of such a signal by the sound card, or more generally by an analog/digital converter, would result in an output signal from which the input analog low-frequency signal cannot be reconstructed. Accordingly, an analog low-frequency signal can be e.g. a DC signal or a signal with one or more important frequency components below the predetermined border frequency of the sound card.
Thus, it is not possible to use such a sound card for measurement of analog low-frequency signals.
U.S. Pat. No. 5,987,541 discloses a computer system with a sound card. In this system, the sound card includes a modulation interface for modulation/demodulation of a digitized speech signal on/from a carrier signal of a predetermined frequency. Thus, an analog speech signal is detected by the sound card, converted into a digitized speech signal and modulated on the carrier signal. This is to use different frequency channels on a computer bus for being used by different peripheral devices at the same time. However, with this computer system, if it is used in the scenario described above, measurement of an analog low-frequency signal is still impossible due to the border frequency of the sound card.
Thus, it is one object of the invention to provide a method for analog/digital converting of at least one analog low-frequency signal with an analog/digital converter which can capture only an analog signal with a frequency within a frequency range above a predetermined border frequency value.
This object is achieved with a method for analog/digital converting of at least one analog low-frequency signal with an analog/digital converter which can capture and convert only an analog signal with a frequency above a predetermined border frequency value, in which at least one analog low-frequency signal and at least one analog high-frequency signal are provided. The analog low-frequency signal is a signal with at least one important frequency component below the predetermined border frequency value according to the above definition, such as a non-audio low-frequency signal or even a direct-current signal, which is to be converted by the analog/digital converter. The analog high-frequency signal is an analog signal having only frequency components above the predetermined border frequency value and within the frequency range of the analog/digital converter. Using the analog low-frequency signal and the analog high-frequency signal, an analog intermediate signal is generated, the analog intermediate signal having a characteristic analog feature with which it is possible to reconstruct the analog low-frequency signal from the analog intermediate signal. In a further step, the analog intermediate signal is converted into a digital intermediate signal, i.e. the analog intermediate signal is digitized in the analog/digital converter. This digitizing is done e.g. by sampling the analog intermediate signal. The thus generated digital intermediate signal has a characteristic digital feature, which makes it possible to determine a digital low-frequency signal from the digital intermediate signal. This characteristic digital feature simply may be the digitized characteristic analog feature. In a last step, the desired digital low-frequency signal is determined from the digital intermediate signal using the characteristic digital feature.
It should be noted that the analog intermediate signal may also have frequency components below the predetermined border frequency value. However, it must have sufficient frequency components above the predetermined border frequency value so that it is possible to reconstruct the analog low-frequency signal from the digitized low-frequency signal after the analog intermediate signal has been captured and digitized by the analog/digital converter and the digital low-frequency signal is determined from the digital intermediate signal.
Therefore, according to the invention it is possible to process, i.e. also to capture and convert, at least one analog low-frequency signal with at least one important frequency component below the predetermined border frequency value of the analog/digital converter.
Furthermore, it is a further object of the invention to provide an analog/digital converter device for analog/digital converting of at least one analog low-frequency signal, the analog/digital converter device being able to process an analog low-frequency signal using an analog/digital converter which can detect only an analog signal with a frequency above a predetermined border frequency value, wherein the analog low-frequency signal has at least one important frequency component below the predetermined border frequency value.
This object is achieved with an analog/digital converter device comprising an analog intermediate signal generating unit. With this analog intermediate signal generating unit, the at least one analog low-frequency signal is mixed with a corresponding analog high-frequency signal.
In this context, when mixing the two signals, one may
add the two signals,
subtract the two signals,
multiply the two signals, or
convolve the two signals.
In general, in this context, the mixing may be any linear or non-linear operation, which is processed on the two signals, as far as this operation results in an analog intermediate signal which fulfills the above explained requirements.
The resulting analog intermediate signal generated by the analog intermediate signal generating unit is input to an analog/digital converter which has a predetermined border frequency value, below which the converter attenuates or cuts off frequencies of the input analog signal. That is, the input of the analog/digital converter is connected to the output of the analog intermediate signal generating unit.
By means of the analog/digital converter, the analog intermediate signal is digitized, i.e. for example sampled, thereby generating a digital intermediate signal. The digital intermediate signal has at least one characteristic digital feature, with which it is possible to determine a digital low-frequency signal from the digital intermediate signal.
The output digital intermediate signal is input to at least one low-frequency determination unit, an input of which is connected to an output of the analog/digital converter. With the low-frequency determination unit it is possible to determine the digital low-frequency signal from the digital intermediate signal using the characteristic digital feature.
Thus, the desired digital low-frequency signal is generated.
The low-frequency determination unit may be implemented as a separate hardware unit. Alternatively, the low-frequency determination unit may also be implemented by a software program, which may be executed by any processor e.g. of a computer system, e.g. by the central processing unit of a computer system, which is then the low-frequency determination unit. In other words, the determination of the digital low-frequency signal from the digital intermediate signal does not necessarily be performed in the sound card itself, but may be performed in a remote processor as well.
The characteristic analog feature may be for example
the amplitude of the analog intermediate signal and/or its derivatives, when using amplitude modulation of the analog low-frequency signal and the analog high-frequency signal,
the frequency of the analog intermediate signal and/or its derivatives, when using frequency modulation of the analog low-frequency signal and the analog high-frequency signal,
the phase of the analog intermediate signal and/or its derivatives, when using phase modulation of the analog low-frequency signal and the analog high-frequency signal,
the pulse of the analog intermediate signal and/or its derivatives, when using pulse modulation of the analog low-frequency signal and the analog high-frequency signal, or
any combination of the characteristic analog features described above.
The characteristic digital feature may be the digitized characteristic analog feature, i.e. for example
the amplitude of the digital intermediate signal and/or its derivatives, when using amplitude modulation,
the frequency of the digital intermediate signal and/or its derivatives, when using frequency modulation,
the phase of the digital intermediate signal and/or its derivatives, when using phase modulation,
the pulse of the digital intermediate signal and/or its derivate, when using pulse modulation, or
any combination of the characteristic digital features described above.
Thus, the characteristic feature, be it the characteristic analog feature or the characteristic digital feature, is enabling the demodulation, i.e. reconstruction of the low-frequency signal, either the analog or the digital low-frequency signal.
Furthermore, the invention provides for an analog intermediate signal generating unit for processing at least one analog low-frequency signal having an important frequency component below a predetermined border frequency value, the intermediate signal generating unit generating an analog intermediate signal such that the analog intermediate signal may be captured by an analog/digital converter, which is able to capture only an analog signal with a frequency within a frequency range above the predetermined border frequency value. The analog intermediate signal generating unit comprises a unit for generating the analog intermediate signal by using at least one analog high-frequency signal, which has a frequency above the predetermined border frequency value.
The analog/digital converter device or the analog intermediate signal generating unit according to the invention are preferably used in conjunction with a sound card. As described above, common sound cards usually have the disadvantage that they cannot be used to capture analog non-audio signals with frequencies below the predetermined border frequency value of the sound card. Thus, the advantage of using the analog/digital converter device or the analog intermediate signal generating unit according to the invention in conjunction with such a sound card becomes apparent. The analog/digital converter device according to the invention will be called in the following xe2x80x9csound card devicexe2x80x9d, if used in conjunction with a sound card.
As the analog high-frequency signal, a sine wave signal having a frequency above the predetermined border frequency value may be used. Preferably, the sine wave signal has a frequency of about 5,000 Hz. It should be noted that many sound cards can capture analog signals in a frequency range from 20 Hz to 20,000 Hz. Thus, choosing a frequency of about 5,000 Hz as a frequency of the high-frequency sine wave signal leads to a good analog/digital conversion with almost no loss of amplitude information due to the attenuation of the analog input signal.
In a further embodiment of the invention, the analog output of the sound card is connected to the input of the analog intermediate signal generating unit. Thus, the sound card, which is in this case a full-duplex sound card, is also used as a signal generator for generating the analog high-frequency signal. Sometimes, the analog output of the sound card is connected to the ground potential and the analog input, also referred to as line-in jack, of the sound card is connected to the ground potential as well. This may disturb subsequent capturing of the analog intermediate signal using the line-in jack of the sound card. To solve this problem, in a further preferred embodiment of the invention an isolation unit, e.g. an isolating transformer, is provided, the input of which is connected to the analog output of the sound card. With the isolation unit, the ground potential of the analog input of the sound card and the ground potential of the analog output of the sound card are isolated from each other. Thus, a problem no longer arises with subsequent capturing of the analog intermediate signal using the line-in jack of the sound card.
The analog/digital converter device according to the invention may also be provided in a video card device or a general multimedia card device, or just as a stand-alone device.
According to a further embodiment of the invention, a plurality of analog low-frequency signals, each having an important frequency component below the predetermined border frequency value and a plurality of analog high-frequency signals, each having a frequency above the predetermined border frequency value, are provided. The analog intermediate signal is in this embodiment generated using the analog low-frequency signals and the respective analog high-frequency signals, wherein the analog intermediate signal has characteristic analog features which make it possible to determine each analog low-frequency signal out of the plurality of the analog low-frequency signals from the analog intermediate signal. The digital intermediate signal has characteristic digital features which make it possible to determine a plurality of digital low-frequency signals from the digital intermediate signal, wherein the plurality of digital low-frequency signals corresponds to said plurality of analog low-frequency signals.
For generating the plurality of analog high-frequency signals, there may be provided one signal generator for generating all of said plurality of analog high-frequency signals, or a plurality of signal generators each of which generates one of said plurality of analog high-frequency signals. Furthermore, the number of signal generators may be more than one but less than the number of analog high-frequency signals to be generated, wherein each signal generator generates some of the plurality of analog high-frequency signals.
In the case of one signal generator being provided, an output of the signal generator is connected to a frequency splitting unit, for example to a plurality of band-pass filters to generate the respective plurality of high-frequency signals.
According to the invention such a single signal generator is preferably embodied by the analog/digital converter used for capturing and converting the analog intermediate signal, and further preferably by the analog/digital converter of the sound card if the analog/digital converter device according to the invention is used as a sound card device. The analog high-frequency signal provided at an analog output of the analog/digital converter, in particular at an analog output of the sound card, is splitted into a plurality of analog high-frequency signals by said frequency splitting unit, each of the plurality of analog high-frequency signals having a frequency above the predetermined border frequency value. Each provided analog high-frequency signal has preferably a unique frequency range.
Furthermore, the respective outputs of the frequency splitting unit, (e.g. the outputs of the said plurality of band-pass filters) may optionally be connected to a plurality of isolation units for the above discussed purposes.
In the case of providing a plurality of signal generators each signal generator may generate an analog high-frequency signal having a frequency above the predetermined border frequency value, wherein the signal generators are connected to an input of the analog intermediate signal generating unit. Each signal generator may comprise an isolation unit to securely divide their outputs from a common potential.
The analog/digital converter device is preferably provided in or for a computer system. It should be noted, that the computer system may be a personal computer, a Macintosh(trademark) computer, a notebook, as well as a palmpilot, etc.